LIS651 lecture 5multiple arrays and databases

Thomas Krichel

2010-02-19

databases

• Databases are collection of data with some organization to them.

• The classic example is the relational database. • But not all database need to be relational

databases.

relational databases

• A relational database is a set of tables. There may be relations between the tables.

• Each table has a number of record. Each record has a number of fields.

• When the database is being set up, we fix – the size of each field – relationships between tables

example: Movie database

ID | title | director | date

M1 | Gone with the wind | F. Ford Coppola | 1963

M2 | Room with a view | Coppola, F Ford | 1985

M3 | High Noon | Woody Allan | 1974

M4 | Star Wars | Steve Spielberg | 1993

M5 | Alien | Allen, Woody | 1987

M6 | Blowing in the Wind| Spielberg, Steven | 1962

• Single table• No relations between tables, of course

problem with this database

• All data wrong, but this is just for illustration.• Name covered inconsistently. There is no way to

find films by Woody Allan without having to go through all spelling variations.

• Mistakes are difficult to correct. We have to wade through all records, a masochist’s pleasure.

Better movie database

ID | title | director | year

M1| Gone with the wind | D1 | 1963

M2| Room with a view | D1 | 1985

M3| High Noon | D2 | 1974

M4 | Star Wars | D3 | 1993

M5| Alien | D2 | 1987

M6| Blowing in the Wind | D3 | 1962

ID | director name | birth year

D1 | Ford Coppola, Francis| 1942

D2 | Allan, Woody | 1957

D3 | Spielberg, Steven | 1942

Relational database

• We have a one to many relationship between directors and film– Each film has one director– Each director has produced many films

• Here it becomes possible for the computer– To know which films have been directed by Woody

Allen– To find which films have been directed by a director

born in 1942

Many-to-many relationships

• Each film has one director, but many actors star in it. Relationship between actors and films is a many to many relationship.

• Here are a few actorsID | sex | actor name | birth year

A1 | f | Brigitte Bardot | 1972

A2 | m | George Clooney | 1927

A3 | f | Marilyn Monroe | 1934

Actor/Movie table

actor id | movie id

A1 | M4

A2 | M3

A3 | M2

A1 | M5

A1 | M3

A2 | M6

A3 | M4

… as many lines as required

Many-to-many relationships

• Each film has one director, but many actors star in it. Relationship between actors and films is a many to many relationship.

• Here are a few actorsID | sex | actor name | birth year

A1 | f | Brigitte Bardot | 1972

A2 | m | George Clooney | 1927

A3 | f | Marilyn Monroe | 1934

Many-to-many relationships

• Each film has one director, but many actors star in it. Relationship between actors and films is a many to many relationship.

• Here are a few actorsID | sex | actor name | birth year

A1 | f | Brigitte Bardot | 1972

A2 | m | George Clooney | 1927

A3 | f | Marilyn Monroe | 1934

Actor/Movie table

actor id | movie id

A1 | M4

A2 | M3

A3 | M2

A1 | M5

A1 | M3

A2 | M6

A3 | M4

… as many lines as required

databases in libraries

• Relational databases dominate the world of structured data

• But not so popular in libraries– Slow on very large databases (such as catalogs)

– Library data has nasty ad-hoc relationships, e.g.• Translation of the first edition of a book

• CD supplement that comes with the print version

Difficult to deal with in a system where all relations and field have to be set up at the start, can not be changed easily later.

databases in web sites• Lots of active web sites are driven by relational

databases. All large active web sites are.• The design of a active web site first involves

looking at databases.• In a shop situation, we have the following tables

– customers– products– orders– orders_products

for multiple to multiple relationship between orders and products.

SQL

• SQL, also pronounced sequel, stands for "structured query language".

• It is a standard language for querying database. • In database speak a query is anything one can do

to a database.

mySQL

• They are a very successful, open-source vendor of SQL software.

• Their product is basically freely available. • We will learn the mySQL dialect of SQL.

phpmyadmin

• phpmyadmin is a set of PHP scripts that create a general purpose interface to work with a mySQL database.

• It is written in PHP. • It lives at http://wotan.liu.edu/phpmyadmin.• You need an account. This is not your wotan

account, but a permission to use a database on the mySQL server running at wotan.

arrays and tables

• Arrays seem to cause the most confusion in student understanding.

• An array is just a way for PHP to address multiple things as one variable.

• Arrays can be of multiple dimensions. • This is typically the case when the array

represents the contents of a table.

example

• Here is an example tablename type brewer rating price

Bruch Festbock dark Bruch good 1.18

Balitka 8 wheat Baltika good 0.88

Budweiser light A.-B. lousy 0.99

• typically, records appear in lines and fields in columns.

arrays and tables

• Arrays seem to cause the most confusion in student understanding.

• An array is just a way for PHP to address multiple things as one variable.

• Arrays can be of multiple dimensions. • This is typically the case when the array

represents the contents of a table.

example

• Here is an example tablename type brewer rating price

Bruch Festbock dark Bruch good 1.18

Balitka 8 wheat Baltika good 0.88

Budweiser light A.-B. lousy 0.99

• typically, records appear in lines and fields in columns.

one way to set out the table

$beers[0]['name']='Bruch Landbock';

$beers[0]['type']='dark';

$beers[0]['brewer']='Bruch‘;

….

$beers[2]['price']=0.99;

• Here, records are a numeric array. Fields are string arrays that are members of the numeric array.

• What instruction would improve the rating of Budweiser?

another way …

$beer=array( 'name'=> 'Bruch Landbock', type=>'dark', 'brewer'=> 'Bruch', 'rating'=>'good', price=>'1.18');

$beers[]=$beer;

…

$beer=array( 'name'=>'Budweiser', type=>'light', 'brewer'=>'A.-B.', 'rating'=>'lousy', price=>0.99);

$beers[]=$beer;

• This will give the same array as before.

yet another way, as a matrix

$names=array('Bruch Landbock', 'Baltika 8','Budweiser');

$types=array( 'dark', 'wheat', 'light' );

$brewers=array( 'Bruch', 'Baltika', 'A.-B.');

$ratings=array( 'good', 'good', 'lousy');

$prices=array(1.18,0.88,0.99);

$beers=array( $names, $types,$brewers,$ratings, $prices);

• What instruction would improve the rating of Budweiser?

another way to set out the table

$names=array('Bruch Landbock', 'Baltika 8','Budweiser');

$types=array( 'dark', 'wheat', 'light' );

$brewers=array( 'Bruch', 'Baltika', 'A.-B.');

$ratings=array( 'good', 'good', 'lousy');

$prices=array(1.18,0.88,0.99);

$beers=array( 'name'=>$names, 'type'=>$types, 'brewer'=> $brewers, 'rating'=>$ratings, 'price'=>$prices);

• What instruction would improve the rating of Budweiser?

another way to set out the table

$names=array('Bruch Landbock', 'Baltika 8','Budweiser');

$types=array( 'dark', 'wheat', 'light' );

$brewers=array( 'Bruch', 'Baltika', 'A.-B.');

$ratings=array( 'good', 'good', 'lousy');

$prices=array(1.18,0.88,0.99);

$beers=array( 'name'=>$names, 'type'=>$types, 'brewer'=> $brewers, 'rating'=>$ratings, 'price'=>$prices);

• What instruction would improve the rating of Budweiser?

multiple arrays• Example

$products[0]['name']="Grosswald Pilsener";

$products[0]['price']=1.56;

$products[1]['name']="Grosswald Export";

$products[1]['price']=1.34;

$products[2]['name']="Bruch Landbier";

$products[2]['price']=1.22;

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